Tests for migratory history of the New Zealand common smelt (Retropinna retropinna (Richardson)) using otolith isotopic composition

Abstract– Stable oxygen and carbon isotopic analyses were made for water at 24 sites, mainly from the Waikato watershed (North Island, New Zealand), and for carbonate from fish sagittal otolith material at each of the sites, mainly from the common smelt ( Retropinna retropinna (Richardson)), to test their potential use in identification of resident and anadromous/migratory stocks suggested in an earlier pilot study. Results provide strong evidence that ¹⁸O is precipitated in otoliths close to isotopic equilibrium with rearing waters. The smelt rearing and residency waters examined have characteristic oxygen and carbon isotopic 'signatures', and the ¹⁸O composition of the smelt otoliths mirrors this within about 1%0, making it possible to use the technique for determining resident and/or migrant history of the fish. The ¹³C otolith composition, though usually tracking that of probable rearing and/or residency waters, has a larger and more variable offset, possibly of metabolic origin, making its use less reliable as a habitat signature.